1. Field of the Invention
The present invention relates to a tunnel magnetoresistive (TMR) effect element, to a thin-film magnetic head with the TMR element, to a magnetic head assembly with the thin-film magnetic head, to a magnetic disk drive apparatus with the magnetic head assembly, to a magnetic memory with the TMR element, and to a manufacturing method of a TMR element.
2. Description of the Related Art
The TMR element has a ferromagnetic tunnel junction structure in which a tunnel barrier layer is sandwiched between a magnetization-fixed layer and a magnetization-free layer. The magnetization-fixed layer has a pinned layer and an anti-ferromagnetic layer (pinning layer). In the magnetization-fixed layer, therefore, the magnetization of the pinned layer is hard to move in response to an external magnetic field due to exchange-coupling field with the anti-ferromagnetic layer. Contrary to this, in the magnetization-free layer, the magnetization is easy to change in response to the external magnetic field. With such a structure, the external magnetic field causes a relative orientation of the magnetization directions of the magnetization-fixed layer and the magnetization-free layer to change. The change of the relative magnetization orientation causes the probability of electrons tunneling through the tunnel barrier layer to vary, to thereby change resistance of the element. Such a TMR element is usable as a read head element that detects intensity of magnetic field from a recording medium, and also applicable to a cell of magnetic RAM (MRAM) as a magnetic memory.
As material of the tunnel barrier layer in the TMR element, amorphous oxide of aluminum (Al) or titanium (Ti) has been generally used as disclosed for example in U.S. Pat. No. 6,710,987.
Recently, there has been proposed a TMR element using a tunnel barrier layer made of crystalline magnesium (Mg) oxide. Such TMR element using the tunnel barrier layer of magnesium oxide can have a higher MR ratio (magnetoresistive change ratio) compared with the TMR element with a tunnel barrier layer of Al oxide or Ti oxide as disclosed in U.S. Patent Publication No. 2006/0056115A1.
The tunnel barrier layer of crystalline oxide such as Mg oxide tends to become the orientation of (001) if it is deposited on an amorphous layer, that is, if its under magnetic layer is made of an amorphous material such as a cobalt iron boron (CoFeB). The orientation of (001) in the tunnel barrier layer of crystalline oxide causes coherent spin-polarized tunneling or single-electron spin-polarized tunneling to increase the MR ratio higher than that when using a tunnel barrier layer of amorphous oxide such as Al oxide.
It is known in this art that an MR ratio of a TMR element using a tunnel barrier layer of crystalline oxide more increases when the CoFeB layer is crystallized by performing an anneal process after a deposition process of these layers. However, in order to crystallize an amorphous CoFeB layer, it is necessary to increase the annealing temperature to an extremely high temperature such as 300° C. or more. Performing of such high temperature annealing process during the manufacturing process of the thin-film magnetic head is not desirable because the magnetization conditions and also the crystalline structure in the shield layers and other layers may change.